[Neuroendocrine expression markers in triple-negative, luminal-A, luminal-B and HER2neu breast cancer].

Background: Primary breast tumors with neuroendocrine (NE) differentiation are a heterogeneous tumor group with diversity of biological behavior, with poorly defined prevalence and prognosis.

Objective: To evaluate the chromogranin, synaptophysin, CD56, INSM1 markers expression prevalence and the association between NE differentiation and tumor molecular type.

Material and methods: Observational, cross-sectional study which included 110 breast tissue samples with primary invasive carcinoma. Immunohistochemistry was performed for chromogranin, synaptophysin, CD56 and INMS1 markers. NE differentiation was considered with 10-90% positive cells, and NE tumor with > 90% positive cells.

Results: 26.3% showed neuroendocrine differentiation. Out of these, 48.2% were luminal-A type, 24.1% luminal-B, 11.5% HER2neu, 17.2% triple-negative; 1.8% were NE tumors. Tumors were marker positive, and out of these to chromogranin in 24.5%, synaptophysin in 28.2%, CD56 in 2.7%, INSM1 in 16.4%. Synaptophysin was expressed in 17.3% luminal-A type, 6.4% luminal-B, 0.9% HER2neu, 3.6% triple-negative. NE differentiation showed association with synaptophysin expression (r = 0.586, p = 0.0001).

Conclusion: The NE differentiation prevalence was 26.3% in primary invasive breast cancers, with luminal-A molecular type predominance.